Pyrolysis gasoline produced from liquid fed ethylene production units (or crackers) contains valuable C5 diolefins such as cis and trans 1,3 Pentadiene (otherwise known as Piperylenes or “Pips”), Isoprene, and Cyclopentadiene (CPD). Current processes in the field are focused on isolating the isoprene from this mixture for making poly isoprene. The heavies such as cis and trans 1,3 pentadienes and the dimer of cyclopentadiene (known as dicyclopentadiene or DCPD) are normally destroyed via hydrogenation either to be blended with gasoline or to recycle as a feed to the cracker. The art of separation has been well known for many decades and uses equipment such as dimer reactors, distillation columns, and extractive distillation methods to obtain the polymer grade isoprene with maximum recovery of isoprene.
DCPD and the 1,3 pentadienes are used as feed stocks in the hydrocarbon resin manufacturing industry. The compositions of these two feed stocks vary depending on the processing details of each liquid cracker. The type of hydrocarbon resin manufactured and is well known to those in the art of making hydrocarbon resins. The piperylene stream traditionally obtained from the C5 fraction does not contain other key reactive monomers essential for making catalytic C5 hydrocarbon resins. Further, the DCPD stream is traditionally operated in a way that minimizes formation of CPD codimers. In fact, the C5 separations design is such that the dimerization system is targeted to minimize the codimers and subsequent loss of isoprene. The design of the C5 separations units is intended for maximum isoprene recovery and heavy molecules such as DCPD and Piperylene are generally rejected/lost in the process of purifying the isoprene.
Isoprene purification systems traditionally involve 2 stage extractive distillation and a sequence of at least 3 purification columns and water wash towers. The products other than isoprene are typically required to be passed through hydrogenation step to saturate problematic alkynes. Prior art processes either concentrate on isoprene purification or removal of alkynes by hydrogenation to upgrade the stream quality. The prior art processes consider the isoprene recovery and DCPD and 1,3 pentadiene recovery in a single coordinated process.